1. Field of the Invention
The invention relates to rotary phase generators for converting one phase A-C power to three phase A-C power.
2. Description of the Prior Art
A rotary phase generator is a rotating machine which has an input of 1 phase AC power; and has an output of 3 phase power. The input and output voltages are essentially the same. The machine may be rated in KVA. The machine is used primarily to operate 3 phase electric motors on 1 phase power. Several motors may be operated on one rotary phase generator. The prior art machines in use at this time consist of a 3 phase motor, a high slip (high resistance) rotor, and running capacitors connected from 1 of 2 phase windings to the 3rd phase winding. The 1 phase power is applied to the first 2 phase windings, and the 3 phase power is taken from all 3 phase windings. The 3rd phase winding acts also as a starting winding. The machine starts and runs similar to a 1 phase, permanent capacitor motor (low starting torque capacitor motor). The high slip motor is used so that the machine will start on the low capacity running capacitors, and once started, the high resistance rotor then becomes a detriment to the machine. The high slip (high resistance) rotor of the motor operates at a higher temperature than a motor with a standard rotor. The high temperature is detrimental to the bearings and other parts of the machine. The high resistance rotor also has a tendency to open up (rotor bars part) more so than a standard (low resistance) rotor, especially when operated at no load or light load. The machine is not very stable at no load or light load as to voltage. To get the machine to hold at a fairly normal voltage at full load, capacitance is added to the capacitor phase. The capacitor phase will then be about 25% higher than the input voltage at no load or light load. Voltage may then be 230/230/287. The rural power companies very often run their voltage as high as 250 volts. The voltage of the machine may then be 250/250/312 at no load or light load. The voltage will drop rapidly on the capacitor phase as the machine is loaded. At full load the voltage on the capacitor phase may be as much as 15% low. The high voltage is detrimental to equipment which does not load the machine very much, and the low voltage at full load is also detrimental to motors operating on the machine. The locked torque of motors operated on a rotary phase generator is very low (less than 100%). A static type phase converter is sometimes used with one or more of the load motors to boost the starting torque when higher starting torque is required.
Rotary phase generators are very useful, and are becoming more valuable as the rural loads increase. These rural power systems are largely 1 phase. Some of the motors being installed in these area are quite large. The need for really dependable and improved rotary phase generator systems is real. There is also a need for these machines not used in rural areas; such as small factories, machine shops, etc., where 3 phase power is not available.